Compressible cap for dowel bars



Dec 22, 1942. R. E. I VIITGH ELL 5, 9

I COMPRESSIBLE. CAP FOR DOWEL BARS Filed Aug. 3, 1940 "Tiwmbm rATTORNEYS Patentecl Dec. 22, 1942 UNITED STATES PATENT OFFICECOMPRESSIBLE CAP FOR DOWEL BARS Robert E. Mitchell, Seattle, Wash.

Application August 3, 1940, Serial No. 350,846

4 Claims. (01. 94-18) My present invention relates to the general art ofconcrete paving and more particularly to a compressible cap for dowelbars.

Where concrete pavement is made in slabs or panels it is necessary tojoin these-panels so as to assure that they will not become displacedand thus permit one to sink below the surface of the other, and thuscause an uneven road surface. The usual method of achieving this resultis to place steel bars at frequent intervals which extend half in oneslab and half in the abutting slab. It has been found, however, that dueto temperature changes there is considerable movement of the slabs.Normally, to provide means for insuring a smooth road surface, the jointbetween the two slabs is filled with an expansion joint material,usually of felt or fibrous base that is impregnated with asphalt or somesimilar substance. Thus, when the pavement becomes heated, it willcontract, and when the pavement shrinks away, the material will tend toshrink back into its normal position. This expansion joint, however,provides an excellent lubricant for the slab edges, and further makesmore acute the necessity for the dowel bars. great shearing strain issometimes placed on the dowel bars themselves, and it becomes necessarythat the ends of the dowel bars not be restricted against movement, orat least, that one end of each dowel bar be free to move into theadjoining slab as expansion occurs.

My device consists essentially in providing a flexible rubber cap whichis adapted to fit on the end of a small bar and to provide means fordisplacing sufiicient of the concrete as the same is being poured sothat a cavity is formed at the end of the dowel bar which will permitits fullest expansion and contraction without injury to the edge of theconcrete slab. This general object is achieved by having the rubber capmade generally in cross-section to the shape of the dowel bar and, byproviding that it fit over the end of the dowel bar, a cavity ofsufiicient size to permit the free movement of the dowel bar is assured.

Many devices have been provided for this purpose. Devices to accomplishthis purpose have been made of metal or paper, but have proved to bedifficult to handle, particularly in wet weather and the like, and areoften subject to serious damage in handling. With my present flexiblecap, being made of a readily yieldable rubber, the caps may be put inplace at their point of manufacture, and then may be transported anddelivered and used without danger of the caps be- With this working ofthe slabs,

coming damaged to the point of not serving their intended purpose.

The principal object of my present invention, therefore, is to provide acavity-producing cap for dowel bars that is made from yieldablematerial.

A further object of my present invention is to provide a yieldablerubber cap for dowel bars that is so arranged interiorly as toaccurately position the cap on the dowel bar.

A further object of my invention is to provide a flexible rubber cap foruse on dowel bars that is so proportioned as to accurately provide acavity of ample proportions to take care of any expansion to which thedowel bar may be subjected.

Other and more specific objects will be apparent from the followingdescription taken in connection with the accompanying drawing, whereinFigure 1 is a perspective view of a rubber cap made after the teachingsof my invention.

Figure 2 is a typical longitudinal section through the same.

Figure 3 is a sectional view similar to Figure 2, but showing a cap inits proper position on a dowel bar, which dowel has, in turn, beensuitably treated for use.

Figures 4, 5 and 6 are cross-sectional views taken along similarlynumbered lines of Figure 3.

Figure 7 is a perspective view showing one half of a modified form of arubber cap with the cutaway portion indicated by dotted lines.

Figure 8 is a perspective view, showing a further modification of mydowel bar cap, the same being cut away so as to show one half of a capwhich has been out along its center in section.

Figure 9 is a perspective view showing another cap made after mypreferred arrangement and illustrating how it is adaptable torectangular dowel bars.

Figure 10 is a perspective view showing the manner in which dowel barsare used, and illustrating the manner in which my caps are employedthereon.

Referring to the drawing, throughout which like reference charactersindicate like parts, l2 designates generally the shell of my cap. This Iprefer to make of rubber of such a temper that it will be resistant todistortion but, under pressure, can be distorted. It should be ofsufiicient rigidity so that the concrete, which is normally poured to adepth of six inches at its extremes over it, will not displace the cap.0n the other hand, it should be sufiiciently fiexible that it can beeasily put on the end 01' a dowel bar. even though the end may not becut accurate and true. The ability of the cap to accommodate asheared-off dowel bar effects a very considerable saving over thosedevices which require that the dowel bars be machined on the ends, as isnormally required when metal tubular caps are employed.

The outer surface and the interior of the cap must, of necessity,conform in section to the section of the dowel bar it is to be usedwith. It should, however, be sufliciently larger than the dowel barso'that there will be ample space for the rubber of the cap to flow ordistort as the dowel bar under expansion tends to fill the chamber inthe end of the cap.

In Figure 7 I have shown a modified form of cap where an adit chamberportion 32 is provided for the reception of the dowel bar and the entirecap is molded from a porous or sponge rubber so that when expansion ofthe dowel bar occurs the rubber mass in the head of the cap, as 34, maybe compressed sufficiently to give adequate clearance for the dowel bar.

In order that my cap may be used to best advantage I have illustrated inFigure the manner in which they are normally employed. In Figure 10 Ihave illustrated two abutting concrete slabs 36 and 31. Into slab 31projects one end of each of the dowel bars 38. The portion of the dowelbar extending into slab 31 is anchored therein by a bond that will besecured with the concrete. This bond will hold the dowel fixedly in thatslab. The portion of the dowel bar in slab 36, exclusive of that portioncovered by the rubber cap, is treated with some form of coating materialor paint 40 which will serve both as a lubricant and to prevent thebonding of the cement to the dowel bar. Normally I provide that thispainting or dipping of the bar extend partly into slab 31 after theshowing in the drawing, so that the dowel bar will be held only for asufiicient length to assure a gripping at one end, but not enough sothat the difference in the coefiicient of expansion between the dowelbar and the concrete will cause the margin of the slab 31 to check orcrack.

It is very essential that the cap be placed on the dowel bar in such amanner that adequate space is provided within the cap for the subsequentmovement of the dowel bar. To assure this, even when the placing of thecap is entrusted to unskilled workmen, definite means are provided toform a section of wall, up against which the dowel bar can be placed andthus ade quate clearance is provided. The preferred arrangement is inproviding a chamber having a plurality of webs l4 which, preferably, mayintersect as is indicated in Figure 4 at 15. A further modifiedarrangement is to provide a substantially annular ring as part of thebody of the cap, as is indicated in Figure 8 at l6. A furthermodification is illustrated in Figure 9, in which one or more webs l8are employed, together with abutments as and 2|. This form isparticularly adaptable to the dowel bars of rectangular cross-section.

Attention is directed to a desirable proportion of the two chambers ofmy cap. The adit chamber as 22, or 24 or 26, as shown in Figures 2, 8and 9, is preferably less in size than the webbed interior ordisplacement chamber shown in the same figures at 28, 29 and 30respectively. This arrangement is desirable in order that an interiordiameter be provided for the reception of the dowel bar on expansionthat will provide also sufficient space for the rubber of the cap whichmay be displaced into that space due to the slight movement of the capunder the end thrust of the dowel bar when expansion occurs.

It will be apparent that with the device installed as illustrated, it isbelieved, that when,

expansion or contraction occurs thedowel bar will be moved by its seatagainst the slab 31 and will be free to move within slab 36, inasmuch asit is not bonded in it. When extreme expansion occurs the dowel bar willbe driven into the flexible rubber cap and into the cavity that the caphas formed in the concrete during the concrete pouring and settingoperation.

The foregoing description and the accompanying drawing are believed toclearly disclose a preferred embodiment of my invention, but it will beunderstood that this disclosure is merely illustrative and that suchchanges in the invention may be made as are fairly within the scope andspirit of the following claims.

Having thus fully described my invention, what I claim as new and desireto secure by Letters Patent is:

1. A cap for use in connection with dowel pins that are positionedbetween expansible members, said cap comprising a resilient elongatedbody having a cup to receive and accommodate a dowel end, and an innerflange medially located in said cup and adapted to space the closed endof the body a distance from an inserted dowel end greater than thethickness of the walls of the body.

2. A cap for use in connection with dowel pins that are positionedbetween expansible members, said cap comprising a resilient elongatedbody having a cup to receive and accommodate a dowel end, and a web inthe inner portion of the cup adapted to space the closed end of the bodya distance from an inserted dowel end greater than the thickness of thewalls of the body.

3. A cap for use in connection with dowel pins that are positionedbetween expansible members, said cap comprising an elongated hollow bodyof resilient material having a single closed end, a member spaced fromthe inner bottom of said hollow body in the path of a dowel end insertedtherein to space the same from said bottom, said member comprising aresilient Web integral with the body.

4. A cap for use in connection with dowel pins that are positionedbetween expansible members, said 'cap comprising an elongated hollowbody of resilient material having a single closed end, a member spacedfrom the inner bottom of said hollow body in the path of a dowel endinserted therein to space the same from said bottom, said membercomprising a cross-shaped resilient web integral with the body.

ROBERT E. MITCHELL.

